CMOS Image Sensor BDTI Etch Stop Structure for Trench Depth Control

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Solution Overview

Problem

The increased trench depth loading in cross-road portions of backside deep trench isolation (BDTI) structures due to higher etch rates results in the likelihood of etching into floating diffusion nodes, leading to pixel sensor failure in CMOS image sensors.

Innovation Solution

Incorporating dielectric etch stop structures in the semiconductor layer to minimize trench depth loading, preventing etching into floating diffusion nodes by ensuring etching stops on these structures in cross-road portions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If higher etch rates are used to increase productivity, then trench formation speed is improved, but trench depth loading increases causing etching into floating diffusion nodes and pixel sensor failure

Engineering Contradiction:

Improvetrench formation speedVSAvoidpixel sensor reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A dielectric etch stop structure is formed in the semiconductor substrate at the cross-road portion before the trench etching process. This preliminary structure prevents the etch plasma from reaching the floating diffusion node by stopping the etching process at the dielectric layer, thereby protecting the pixel sensor while allowing higher etch rates to be used for improved productivity

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If etching continues deeper to remove excess material, then manufacturing precision is improved, but floating diffusion nodes are damaged leading to pixel sensor failure

Engineering Contradiction:

Improvetrench depth controlVSAvoiddamage to floating diffusion nodes

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The dielectric etch stop structure acts as an intermediary layer between the trench and the floating diffusion node. It provides a physical barrier that stops the etching process before it can damage the floating diffusion node, while still allowing sufficient trench depth to be achieved for proper isolation functionality

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Reduces the likelihood of pixel sensor failure and maintains performance by protecting floating diffusion nodes, enhancing etching precision and sensor efficiency.

Implementation Method 1

dielectric regions may function as etch stop structures in the cross-road portions

Methodology Applied

Scientific EffectEtch stop:

Implementation Method 2

a photodiode configured to convert photons of incident light into a photocurrent of electrons

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20250275277A1Image sensor device and methods of formation

Publication Date: 2025.08.28 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Dielectric regions are formed in a semiconductor substrate of a semiconductor device. The dielectric regions may be formed in locations above which cross-road portions of a backside deep trench isolation (BDTI) structure are to be formed for a pixel sensor array of the semiconductor device. The dielectric regions may function as etch stop structures in the cross-road portions when etching the semiconductor substrate to form the trenches in which the BDTI structure is to be formed. In particular, the dielectric regions minimize and/or prevent the increase in trench depth of the trenches in the cross-road portions relative to the trench depth of the trenches in the non-cross-road portions.